Diffusion Mode Research Articles (Page 3)

This paper reports the experimental results of the vortex-induced vibration (VIV) of a flexible submarine pipe conveying gas flow with the presence of small-hole gas leakage from its mid-span. The tests were conducted in a recirculation water flume in the reduced velocity range of Ur = 1.16–10.65 using the non-intrusive measurement, corresponding to the Reynolds number range of Re = 133–1218. The vibration characteristics of the pipe span with an aspect ratio of 95 in the cases of four leakage orientations (θ) and three conveyed gas flow rates (Q) are examined as well as the gas diffusion to reveal the interaction between the VIV and gas leakage. The experimental results indicate that the presence of gas leakage enhances the VIV, accompanied by the reduction in the onset Ur for vibration. The gas diffusion behavior is related to the pipe vibration as well as the incoming flow velocity. In particular, the gas bubble coalescence is observed in the wake in small Ur cases when the leakage rate is relatively large. Furthermore, as Ur increases, the discharged gas bubbles migrate in clusters, suggesting a noticeable correlation with the pipe vibration cycle. In the considered Ur range, five gas diffusion modes are identified based on the amount of gas bubbles, the occurrence of bubble coalescence and the correlation with pipe vibration, and the partition of diffusion modes is provided in the Q–Ur and θ–Ur maps.

The diffusion of nano-confined fluids plays a crucial role in nano-energy research. We developed three molecular models to calculate the diffusion behavior of both supercritical water (SCW) at 673–1173 K, 250 atm, and room water (300 K, 1 atm), confined in carbon nanotubes (CNTs) ranging from 9.49 to 50.17 Å. We analyzed the diffusion mechanism of water confined in various CNTs using the time coefficient. We calculated the self-diffusion coefficient of water in Fickian-like diffusion mode and examined the factors influencing it. The results indicate that in small-diameter CNT (7,7), SCW primarily follows a Fickian-like diffusion mode, while room temperature (300 K, 1 atm) water exhibits a superdiffusion mode. For CNT diameters larger than 20 Å, both room temperature water and SCW predominantly exhibit Fickian-like diffusion. Additionally, the self-diffusion coefficient of SCW increases linearly with temperature, displaying clear Arrhenius behavior. The self-diffusion activation energy of SCW in different types of CNTs shows a strong correlation with the hydrogen bond structure. Finally, we combined the saturated relationship between CNT diameter and self-diffusion coefficient to propose a predictive model for the self-diffusion coefficient of confined SCW. The model is simple, requiring only three parameters, with a mean absolute relative error of less than 6.5%.

Diffusion law and diffusion model for backfill grouting in loess shield tunnel at different soil moisture

Abstract Metaheuristic algorithms are extensively utilized in engineering due to their outstanding capacity for solving optimization problems with restricted computing resources or incomplete data. However, its extended use is constrained by the low optimization accuracy and premature convergence. The rapid spread and extensive reach of the COVID-19 virus have inspired the proposal of a new virus diffusion algorithm (VDA) to overcome the limitations of the metaheuristic algorithm. This article utilizes the VDA algorithm to segment spun cracks, providing a method for intelligent detection of spinning process. The algorithm integrates global diffusion and local diffusion mechanisms to simulate both the random walk and local disturbance modes of virus diffusion, thereby enhancing its accuracy. Additionally, it introduces the competition mechanism and infection center rate to enhance the diversity of the population and expand the algorithm’s search range. The effectiveness and robustness of the VDA algorithm is validated using the CEC’17 test benchmark function. Subsequently, the VDA algorithm is used to segment images with cracks in thin-walled spun parts. The experimentally obtained results illustrate that the VDA-based segmentation algorithm attains a PSNR of 23.6798 and an SSIM of 0.9864 for crack images, surpassing other segmentation algorithms in challenging conditions.

The thermal conductivity κ of solid CO2 was studied in the temperature T range of 100–220 K and at pressures up to 200 MPa using the transient hot-wire method. The results are consistent with those expected for a polycrystal composed of small molecules, with κ increasing significantly as the temperature decreases and as pressure and density increase. The variation in κ with temperature is primarily attributed to changes in phonon–phonon scattering and density. The thermal conductivity behaviour is described using a two-basis model, where heat is transported by both phonons and diffuse modes. The density ρ dependence of the thermal conductivity, represented by the Bridgman parameter g = (d ln κ/d ln ρ)T, was found to be g = 6.7 at 190 K, increasing to 9.4 at 110 K as the temperature decreases. This increase is attributed to an enhanced phonon contribution to the total κ.

Nondiffusive effects in charge transport become relevant as device sizes and features become comparable to the electronic mean free path. As a model system, we investigated the electric transport around mesoscopic defects in graphene with scanning tunneling potentiometry. Diffusive and ballistic contributions to the scattering dipole are probed by simultaneously resolving the nanoscale topography of pits in the graphene layer and measuring the local electrochemical potential in the surrounding area. We find evidence of transport in the intermediate regime between the diffusive and ballistic limits such that the magnitude of the electrochemical potential around the defects is substantially underestimated by diffusive models. Our experiments and modeling are supported by lattice-Boltzmann simulations, which highlight the importance of the ratio between defect size and mean free path in the intermediate transport regime. The magnitude of the scattering dipole depends on the shape of the pits in both the ballistic and diffusive transport modes. Remarkably, ballistic contributions to the electron transport are found at feature sizes larger than the mean free path and rapidly increase at lower sizes, having a noticeable impact already on mesoscopic length scales.

Radiation plays a significant role in solar and astrophysical environments, as it may constitute a sizable fraction of the energy density, momentum flux, and total pressure. Modeling the dynamic interaction between radiation and magnetized plasmas in such environments is an intricate and computationally costly task. The goal of this work is to demonstrate the capabilities of the open-source parallel, block-adaptive computational framework MPI-AMRVAC in solving equations of radiation-magnetohydrodynamics (RMHD) and to present benchmark test cases relevant for radiation-dominated magnetized plasmas. We combined the existing magnetohydrodynamics (MHD) and flux-limited diffusion (FLD) radiative-hydrodynamics physics modules to solve the equations of RMHD on block-adaptive finite volume Cartesian meshes in any dimensionality. We introduce and validate several benchmark test cases, such as steady radiative MHD shocks, radiation-damped linear MHD waves, radiation-modified Riemann problems, and a multi-dimensional radiative magnetoconvection case. We recall the basic governing Rankine-Hugoniot relations for shocks and the dispersion relation for linear MHD waves in the presence of optically thick radiation fields where the diffusion limit is reached. The RMHD system allows for eight linear wave types, where the classical seven-wave MHD picture (entropy and three wave pairs for slow, Alfv'en and fast) is augmented with a radiative diffusion mode. The MPI-AMRVAC code now has the capability to perform multidimensional RMHD simulations with mesh adaptation, making it well suited for larger scientific applications studying magnetized matter-radiation interactions in solar and stellar interiors and atmospheres.

Resolving the Mystery of the Extraordinary Polyelectrolyte Behavior (Anomalously Slow Diffusive Mode) after Half-Century of Research

ABSTRACT This paper develops a simple model of academic research to analyze knowledge flows within a research system, when demand for multi-disciplinarity varies. Scientists are embedded in departments, linked to all others in the department, as well as to a small number of others outside the department. Pairs of scientists collaborate to produce ‘papers’. They can collaborate successfully with their direct links provided the distances in knowledge space between partners are within specified upper and lower bounds. By creating new knowledge, co-authors converge in their knowledge endowments, and the distance between them can fall below the lower bound. This is mitigated in two ways: extra-departmental links; and an intermittent job market in which scientists can change departments. In a simulation model we find that increasing the extent of extra-departmental links, and increasing job market activity both improve aggregate knowledge production. These two modes of knowledge diffusion are, however, substitutes rather than complements: increasing both does not improve performance over increasing only one. In addition, we find that increasing demands for multi-disciplinarity (essentially increasing the lower bound on knowledge distance for effective collaboration) generally decreases knowledge production.

The hydrodynamics of crystals with vacancies is developed on the basis of local-equilibrium thermodynamics, where the chemical potential of vacancies plays a key role together with a constraint relating the concentration of vacancies to the density of mass and the strain tensor. The microscopic foundations are established, leading to Green-Kubo and Einstein-Helfand formulas for the transport coefficients, including the vacancy conductivities and the coefficients of vacancy thermodiffusion. As a consequence of having introduced the chemical potential of vacancies, a relationship is obtained between the conductivities and the Fickian diffusion coefficients for the vacancies. The macroscopic equationsare linearized around equilibrium to deduce the dispersion relations of the eight hydrodynamic modes. The theoretical predictions are confirmed by numerical simulations of the hard-sphere crystal with vacancies. The study explicitly shows that the eighth hydrodynamic mode of nonperfect monatomic crystals is indeed a mode of vacancy diffusion.

Diffuse background illumination (DBI) diagnostics is applied to study spray instabilities in lean direct injection combustion systems for gas turbines. Experiments were performed in a reacting kerosene spray at atmospheric pressure using DBI, Mie Scattering, and OH* chemiluminescence (OH*-CL) imaging to delineate instability dynamics. Comparison of DBI and Mie scattering results shows that the Mie scattering is effective in illustrating the planar structure of the dispersed spray, but the line-of-sight DBI provided an improved visualization of the off-axis features of the spray to aid in understanding the spray dynamics. Measurements were postprocessed into phase-reconstructed data to illustrate the dynamic relationship between spray and OH*-CL oscillations and to demonstrate the effectiveness of DBI imaging for illustrating the influence of spray structure on the flame topology. Results show that DBI provides a clear illustration of how spray oscillations govern the switching between premixed (lean or rich) and diffusion modes of combustion over the course of the oscillation cycle.

Fe-exchanged zeolites are heterogeneous catalysts that can potentially ensure simultaneous conversion of nitrous oxide (N2O) and nitric oxide (NO) using ammonia (NH3) as a selective reducing agent through their selective catalytic reduction reaction (N2O-NO-SCR). In this study, we rationalize the origin of the beneficial effect of N2O on the NO conversion by combining catalytic experiments with ex situ characterization and in situ/operando X-ray absorption spectroscopy (XAS) and infrared spectroscopy in diffuse reflectance mode (DRIFTS) on a series of Fe-ZSM-5 catalysts where we attempted to control Fe speciation at constant Fe content. The catalytic activity data revealed that N2O can promote NO conversion at different temperatures and to different extents. This behavior was found to be related to the activity of the catalysts in the NO-mediated N2O decomposition reaction, which ensures the oxidative transformation of NO and thus sustains the N2O-NO-SCR chemistry. The oxidation activity is in turn determined by processes of N2O activation and NO adsorption, which are a function of the Fe speciation and are likely catalyzed by a minority of isolated Fe2+ sites coordinated in different cationic environments. In agreement, the concentrations of the Fe species able to activate N2O (Cα) and of the Fe species able to coordinate NO (CFe-NO) decrease with an increasing degree of Fe agglomeration and govern especially the promotion of the NO conversion induced by N2O in this dual-site mechanism. Maximization of the concentration of both species is therefore essential to design Fe-exchanged zeolites with the highest activity toward the N2O-NO-SCR reaction.

Single-particle tracking has enabled quantitative studies of complex systems, providing nanometer localization precision and millisecond temporal resolution in heterogeneous environments. However, at micro- or nanometer scales, probe dynamics become inherently stochastic due to Brownian motion and complex interactions, leading to varied diffusion behaviors. Typically, analysis of such trajectory data involves certain moving-window operation and assumes the existence of some pseudo-steady states, particularly when evaluating predefined parameters or specific types of diffusion modes. Here, we introduce the stochastic particle-informed neural network (SPINN), a physics-informed deep learning framework that integrates stochastic differential equations to model and infer particle diffusion dynamics. The SPINN autonomously explores parameter spaces and distinguishes between deterministic and stochastic components with single-frame resolution. Using the anomalous diffusion dataset, we validated SPINN's ability to reduce frame-to-frame variability while preserving key statistical correlations, allowing for accurate characterization of different stochastic processes. When applied to the diffusion of single gold nanorods in hydrogels, the SPINN revealed enhanced microrheological properties during hydrogel gelation and uncovered interfacial dynamics during dextran/tetra-PEG liquid-liquid phase separation. By improving the temporal resolution of stochastic dynamics, the SPINN facilitates the estimation and prediction of complex diffusion behaviors, offering insights into underlying physical mechanisms at mesoscopic scales.

The different modes of the spin dynamics in ferrimagnetic magnetite iron oxide nanoparticles (Fe3O4) have been addressed by µeV neutron spectroscopy for particles with a diameter of 75 ± 18 Å. In an approach building on intensity considerations over a wide range of wave vectors Q in combination with diffusion dynamics, we identify three magnetic modes prevailing in distinct Q regimes up to 1.7 Å−1: (i) Evaluating the structure factor of quasielastic magnetic intensity enables to identify uniquely longitudinal superparamagnetic spin fluctuations in the small Q regime <0.5Å−1, (ii) individual spin relaxation with quasielastic intensity albeit of low intensity is present in two Q ranges of 0.5 Å−1<Q<1.0Å−1 and 1.5 Å−1<Q<1.7Å−1, and (iii) a surprisingly low-energy inelastic spin excitation of 23.2 µeV in magnetite IONPs is found at 150 K in the magnetic Bragg region between 1.1 Å−1<Q<1.4Å−1. Its temperature dependence suggests a collapse of the coherent transverse magnetic fluctuations and a transition into a generalized diffusive mode at about 500 K. Published by the American Physical Society 2025

Pair correlation microscopy is a unique approach to fluorescence correlation spectroscopy that can track the long-range diffusive route of a population of fluorescent molecules in live cells with respect to intracellular architecture. This method is based on the use of a pair correlation function (pCF) that, through spatiotemporal comparison of fluctuations in fluorescence intensity recorded throughout a microscope data acquisition, enables changes in a molecule's arrival time to be spatially mapped and statistically quantified. In this protocol, we present guidelines for the measurement and analysis of line scan pair correlation microscopy data acquired on a confocal laser scanning microscope (CLSM), which will enable users to extract a fluorescent molecule's transport pattern throughout a living cell, and then quantify the molecular accessibility of intracellular barriers encountered or the mode of diffusion governing a molecular trafficking event. Finally, we demonstrate how this protocol can be extended to a two-channel line scan acquisition that, when coupled with a cross pCF calculation, enables a fluorescent molecule's transport pattern to be selectively tracked as a function of complex formation with a spectrally distinct fluorescent ligand. For a skilled user of a CLSM, the line scan data acquisition and analysis described in this protocol will take ~1-2 d, depending on the sample and the number of experiments to be processed.

ABSTRACT By investigating Hong Kong labour organisations’ brokerage practices, this study highlights a mode of vertical diffusion conditioned by geopolitics. Hong Kong is a global city located at the dual peripheries of the West and mainland China. Activists leverage Hong Kong’s location shaped by geopolitics to shift the scale of labour movements in mainland China. Downwards, they use the geographical, historical, cultural, and linguistic proximities of Hong Kong and mainland China to build solidarity in translocal networks, and adapt global action tactics to local contexts. Upwards, activists also connect China’s labour movement with global solidarity networks by engaging in trans-border witnessing and advocacy, and diffusing the action tactic of collective bargaining developed in mainland China to labour politics in other Global South countries. However, the vertical diffusion of social movements is conditioned by geopolitical dynamics, which result in an asymmetrical scale shift of labour politics.

BackgroundThe relict gull (Larus relictus, Charadriiformes, Laridae) classified as vulnerable in the IUCN Red List is defined as a first-class national protected bird in China. However, our knowledge of the evolutionary history of L. relictus is limited. Here, we performed whole-genome resequencing of L. relictus (n = 14) and L. brunnicephalus (n = 3) to explore the genetic relationships and population structures and understand their adaptive evolution.ResultsThe whole genome resequencing generated 667.55 Gb clean reads with an average sequencing depth of ~ 29×. The genomic variant analysis identified 13,717,267 heterozygous SNPs in the samples obtained from 17 individuals. Population genetic diversity analysis revealed that low nucleotide diversity (0.00029) and no obvious population structure in L. relictus. Demographic history revealed that from 180 to 5 kya (thousand years ago), the effective population size (Ne) of L. relictus exhibited declines (24,000 to 5,000), with a very low range population size (2,200 to 5,000). In contrast, from 100 to 80 kya, L. brunnicephalus peaked in ancestral Ne, followed by distinct declines at ~ 70 kya (100,000 to 16,000). The findings identified several genes associated with the correlated changed life-history traits of L. relictus, including BMP4 involved in beak adaptation; HAND2, NEUROG1, COL11A2, and EDNRB involved in the evolution of the palate, soft palate, and tongue; PIGR and PLCB2 involved in an enhanced response to bitter taste by sensing chemical secretions released by staple food substrate insects to activate protective mechanisms. Furthermore, thirty-four genes related to sperm development and activity, including KLHL10 and TEKT3, were identified in the expanded gene family. In addition, MED1, CNOT9, NR5A1, and PATZ1 were involved in enhanced male hormone secretion and a high density of candidate genes associated with embryonic development were identified. The findings indicated that the L. relictus population was in a male-biased diffusion mode; the function of the TEKT3 gene showed that males played a dominant role in brooding, which enhanced their attraction to females. Our study revealed that significant enrichment of olfactory signaling pathway genes, including OR14C36, OR14J1, OR14I1, and OR14A16; inner ear development-related, including PTN, PTPN11, GATA2, ATP8B1, and MYO15A; and those related to hypoxic adaptation to high-altitude breeding and iris colour.ConclusionsBased on the results and the knowledge of this organism biology and habitat use, we infer that less adaptive evolutionary pressure on vision in L. relictus were related with their feeding behaviour and adaptation. In summary, this comprehensive analysis provides insights into the evolutionary features of L. relictus and a new perspective for scientific research on L. relictus to effectively determine its future survival viability.

Currently, the development of highly active photocatalytic additives for self-cleaning cement materials is a topical direction of building materials science. Mixed transition metal oxides are one of the effective types of photocatalysts, because they have improved functional characteristics compared to monometallic compounds. The purpose of this study was to establish the effects of synthesis conditions on the structure parameters and photocatalytic activity of zinc-titanium layered double hydroxide (Zn-Ti LDH) with Zn2+/Ti4+ molar ratio of 2/1, as well as its calcination products in the form of zinc-titanium mixed metal oxides (Zn-Ti MMOs). It was found that the mixing temperature of solutions of precursor salts and precipitators, as well as the temperature of sediment aging, were the main synthesis parameters that had the greatest impact on the phase composition and crystallite size of layered double hydroxide. The research results showed differences in the kinetics of photodestruction of methylene blue (MB) in solution under UV radiation in the presence of Zn-Ti layered double hydroxide and Zn-Ti mixed metal oxides. The photocatalytic process involving Zn-Ti MMOs, corresponding to a pseudo-first order reaction kinetic, proceeded in a diffusion mode with limiting step in the form of dye adsorption on the surface of photocatalyst. The photodegradation of MB in the presence of Zn-Ti LDH, which was more accurately described by a pseudo-second order model, occurred in a kinetic regime, where the photocatalytic reaction was the limiting stage. Mixed metal oxides of zinc and titanium had significantly higher functional characteristics compared to their Zn-Ti LDH precursor. The calcination of Zn-Ti layered double hydroxide at 200–500 °C allowed to achieve the highest photocatalytic activity of Zn-Ti MMO, which was due to phase transformations occurring during thermal treatment. The decomposition of Zn-Ti LDH at 200–250 °C resulted in the formation of a crystalline phase of zinc oxide (ZnO), which had a hexagonal wurtzite crystal structure with the ability to effectively absorb radiation from almost the entire UV spectral region. The rise of the Zn-Ti LDH calcination temperature to 500 °C led to an increase in the crystallinity degree of ZnO.

It is argued that the specific heat of amorphous solids at low temperatures can be understood to arise from a single branch of collective modes. The idea is illustrated in a model of a correlated spin glass for which magnetic anisotropies are present but they are completely frustrated by disorder. The low-energy spectrum is dominated by soft modes corresponding to propagating Halperin–Saslow spin waves at short wavelengths, evolving into a relaxation and a diffusion mode at the long wavelengths. The latter gives rise to an anomalous temperature behavior of the specific heat at T≪T∗: C∼T in d=3 solids, C∼Tln⁡(1/T) in d=2. The temperature scale T∗ has a non-trivial dependence on the damping coefficient describing magnetic friction, which can be related to fluctuations of the spin-torque operator via a Green–Kubo formula. Halperin–Saslow modes can also become diffusive due to disclination motion (plastic flow). Extensions of these ideas to other systems (including disordered phases of correlated electrons in cuprate superconductors and of moiré superlattices) are discussed.

Semiconductor nanomaterials and nanostructured interfaces have important technological applications, ranging from fuel production to electrosynthesis. Their photocatalytic activity is known to be highly heterogeneous, both in an ensemble of nanomaterials and within a single entity. Photoelectrochemical imaging techniques are potentially useful for high-resolution mapping of photo(electro)catalytic active sites; however, the nanoscale spatial resolution required for such experiments has not yet been attained. In this article, we report photoreactivity imaging of two-dimensional MoS2 photocatalysts by two modes of photoscanning electrochemical microscopy (photo-SECM): diffusion and tunneling-based modes. Diffusion-based (feedback mode) photo-SECM is used to map the electron transfer and hydrogen evolution rates on mixed-phase MoS2 nanosheets and MoS2 chemical vapor deposition (CVD)-grown triangles. An extremely high resolution of photoelectrochemical imaging (about 1-2 nm) by the tunneling mode of the photo-SECM is demonstrated.